U.S. patent number 10,604,131 [Application Number 16/034,735] was granted by the patent office on 2020-03-31 for open loop control for electromechanical brake.
This patent grant is currently assigned to ROBERT BOSCH GMBH. The grantee listed for this patent is Robert Bosch GmbH. Invention is credited to Karsten Bieltz.
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United States Patent |
10,604,131 |
Bieltz |
March 31, 2020 |
Open loop control for electromechanical brake
Abstract
Systems and methods for providing open loop motor control for an
electromechanical brake when closed loop motor control fails. The
method includes determining, with an electronic controller, whether
a rotor position sensor or a current sensor is not operating
correctly, generating, with the electronic controller, a generated
control signal for controlling a permanent magnet synchronous
machine, and activating, with the electronic controller, the
permanent magnet synchronous machine using the generated control
signal to generate a stator magnetic field to operate the rotor of
the permanent magnet synchronous machine of the electromechanical
brake.
Inventors: |
Bieltz; Karsten (Mundelsheim,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
N/A |
DE |
|
|
Assignee: |
ROBERT BOSCH GMBH (Stuttgart,
DE)
|
Family
ID: |
67137953 |
Appl.
No.: |
16/034,735 |
Filed: |
July 13, 2018 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20200017093 A1 |
Jan 16, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T
8/00 (20130101); H02P 6/24 (20130101); B60T
8/885 (20130101); H02P 21/0003 (20130101); H02P
6/12 (20130101); B60T 13/662 (20130101); B60T
13/143 (20130101); H02P 29/028 (20130101); B60T
2270/402 (20130101); B60T 8/3265 (20130101); B60T
8/17 (20130101); B60T 2270/404 (20130101); B60T
13/745 (20130101) |
Current International
Class: |
H02P
6/12 (20060101); H02P 6/24 (20060101); B60T
13/66 (20060101); B60T 13/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
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105197002 |
|
Dec 2015 |
|
CN |
|
102016210369 |
|
Jan 2017 |
|
DE |
|
2009124870 |
|
Jun 2009 |
|
JP |
|
Primary Examiner: Duda; Rina I
Attorney, Agent or Firm: Michael Best & Friedrich
LLP
Claims
What is claimed is:
1. A system for providing open loop motor control for an
electromechanical brake when closed loop motor control fails, the
system comprising: an electromechanical brake mechanism including a
permanent magnet synchronous machine, a rotor position sensor
configured to detect a position of a rotor of the permanent magnet
synchronous machine, a motor current sensor, and an electronic
controller configured to determine whether at least one of the
rotor position sensor and the motor current sensor is not operating
correctly, generate a control signal for controlling the permanent
magnet synchronous machine, wherein the control signal includes a
stator magnetic flux strength, a frequency of the stator magnetic
field, and a specified angular velocity of the stator magnetic
field, and activate the permanent magnet synchronous machine using
the generated control signal to generate a stator magnetic field to
operate the rotor of the permanent magnet synchronous machine.
2. The system of claim 1, further comprising a master cylinder
pressure sensor.
3. The system of claim 2, wherein the electronic controller
receives a master cylinder pressure from the master cylinder
pressure sensor and sets the stator magnetic flux strength of the
permanent magnet synchronous machine based upon the master cylinder
pressure sensor.
4. The system of claim 1, wherein the stator magnetic flux strength
is set, with the electronic controller, by applying a stator
voltage space vector.
5. The system of claim 1, wherein the rotor of the permanent magnet
synchronous machine rotates synchronously with the stator magnetic
field of the permanent magnet synchronous machine.
6. The system of claim 1, wherein an internal torque of the
permanent magnet synchronous machine is controlled, with the
electronic controller, to be higher than a load torque of the
permanent magnet synchronous machine.
7. The system of claim 1, wherein the electronic controller limits
a maximum allowable motor speed gradient in order to prevent the
rotor of the permanent magnet synchronous machine from becoming
asynchronous with the stator magnetic field.
8. The system of claim 7, wherein the maximum allowable motor speed
gradient is based upon a maximum allowable frequency of the stator
magnetic field.
9. The system of claim 7, wherein a maximum allowable motor speed
gradient is based upon a power supply voltage.
10. A method of providing open loop motor control for an
electromechanical brake when closed loop motor control fails, the
method comprising: determining, with an electronic controller,
whether a rotor position sensor or a current sensor is not
operating correctly, generating, with the electronic controller, a
generated control signal for controlling a permanent magnet
synchronous machine, wherein the generated control signal includes
a stator magnetic flux strength, a frequency of the stator magnetic
field, and a specified angular velocity of the stator magnetic
field, and activating, with the electronic controller, the
permanent magnet synchronous machine using the generated control
signal to generate a stator magnetic field to operate the rotor of
the permanent magnet synchronous machine.
11. The method of claim 10, further comprising receiving, with the
electronic controller, a master cylinder pressure from a master
cylinder pressure sensor.
12. The method of claim 11, setting, with the electronic
controller, the stator magnetic flux strength of the permanent
magnet synchronous machine based upon the master cylinder pressure
sensor.
13. The method of claim 10, further comprising setting, with the
electronic controller, the stator magnetic flux strength of the
permanent magnet synchronous machine by applying a stator voltage
space vector.
14. The method of claim 10, wherein the rotor of the permanent
magnet synchronous machine rotates synchronously with the stator
magnetic field of the permanent magnet synchronous machine.
15. The method of claim 10, further including controlling, with the
electronic controller, an internal torque of the permanent magnet
synchronous machine to be higher than a load torque of the
permanent magnet synchronous machine.
16. The method of claim 10, further including limiting, with the
electronic controller, a maximum allowable motor speed gradient in
order to prevent the rotor of the permanent magnet synchronous
machine from becoming asynchronous with the stator magnetic
field.
17. The method of claim 16, wherein the maximum allowable motor
speed gradient is based upon a maximum allowable frequency of the
stator magnetic field.
18. The method of claim 16, wherein a maximum allowable motor speed
gradient is based upon a power supply voltage.
Description
Embodiments relate to systems and methods for providing limited
open loop control to an electromechanical brake when a closed loop
control system fails.
BACKGROUND
In modern braking systems, vacuum brakes are being replaced by
electromechanical and vacuum-free brakes (for example, the iBooster
brake created by Robert Bosch GmbH). Electromechanical and
vacuum-free brakes only use electrical energy during application of
the brakes, which saves fuel and reduces CO.sub.2 emissions of the
vehicle because energy from the combustion engine is not required
to apply more pressure to the brakes.
Electromechanical brakes are controlled based upon sensor input
(for example, a brake pedal travel sensor, a permanent magnet
synchronous machine rotor position sensor, an permanent magnet
synchronous machine current sensor, and the like). An electronic
controller that controls the electromechanical brake receives
feedback from the sensors in order to correctly operate the
electromechanical brake. If the electronic controller does not
receive feedback or receives faulty signals from the sensors, the
electromechanical brake may be incorrectly controlled or not
activated at all.
SUMMARY
Therefore, a system is needed to provide limited open loop control
of the electromechanical brake in case a sensor in a closed loop
control system fails.
One embodiment provides a system that implements open loop motor
control for an electromechanical brake when closed loop motor
control fails. The system includes an electromechanical brake
mechanism including a permanent magnet synchronous machine, a rotor
position sensor configured to detect a position of a rotor of the
permanent magnet synchronous machine, a motor current sensor, and
an electronic controller configured to determine whether at least
one of the rotor position sensor and the motor current sensor is
not operating correctly, generate a control signal for controlling
the permanent magnet synchronous machine, and activate the
permanent magnet synchronous machine using the generated control
signal to generate a stator magnetic field to operate the rotor of
the permanent magnet synchronous machine.
One embodiment provides a method for providing open loop motor
control for an electromechanical brake when closed loop motor
control fails. The method includes determining, with an electronic
controller, whether a rotor position sensor or a current sensor is
not operating correctly, generating, with the electronic
controller, a generated control signal for controlling a permanent
magnet synchronous machine, and activating, with the electronic
controller, the permanent magnet synchronous machine using the
generated control signal to generate a stator magnetic field to
operate the rotor of the permanent magnet synchronous machine of
the electromechanical brake.
Other aspects, features, and embodiments will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a vehicle that includes a braking system
according to one embodiment.
FIG. 2 illustrates an electromechanical braking mechanism according
to one embodiment.
FIG. 3 illustrates an electronic controller according to one
embodiment.
FIG. 4 illustrates a closed-loop method of controlling an
electromechanical braking mechanism according to one
embodiment.
FIG. 5 illustrates an open-loop method of controlling an
electromechanical braking mechanism according to one
embodiment.
DETAILED DESCRIPTION
Before any embodiments are explained in detail, it is to be
understood that this disclosure is not intended to be limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. Embodiments are capable of other
configurations and of being practiced or of being carried out in
various ways.
A plurality of hardware and software based devices, as well as a
plurality of different structural components may be used to
implement various embodiments. In addition, embodiments may include
hardware, software, and electronic components or modules that, for
purposes of discussion, may be illustrated and described as if the
majority of the components were implemented solely in hardware.
However, one of ordinary skill in the art, and based on a reading
of this detailed description, would recognize that, in at least one
embodiment, the electronic based aspects of the invention may be
implemented in software (for example, stored on non-transitory
computer-readable medium) executable by one or more processors. For
example, "control units" and "controllers" described in the
specification can include one or more electronic processors, one or
more memory modules including non-transitory computer-readable
medium, one or more input/output interfaces, one or more
application specific integrated circuits (ASICs), and various
connections (for example, a system bus) connecting the various
components.
FIG. 1 illustrates a vehicle 100 including a braking system 105.
The braking system 105 includes an electromechanical braking
mechanism 110 and an electronic controller 115. The
electromechanical braking mechanism 110 is communicatively coupled
to the electronic controller 115 and hydraulically coupled to
brakes 120-123, which are configured to be applied to wheels
125-128.
In the embodiment illustrated by FIG. 1, the vehicle 100 is a
four-wheeled vehicle, such as an automobile, bus, and the like.
However, it is to be understood that the braking system 105 may be
implemented in other vehicles with more or less wheels (for
example, in a motorcycle).
An example of the electromechanical braking mechanism 110 is
illustrated in FIG. 2.
The electromechanical braking mechanism 110 includes an input rod
205, a travel sensor 210, a permanent magnet synchronous machine
215, a gear system 220, a boost element 225, and a master cylinder
230.
The input rod 205 receives input from an operator of the vehicle
100 to actuate the rest of the electromechanical braking mechanism
110. For example, the input rod 205 may be connected to a brake
pedal, which is depressed by the operator of the vehicle 100 in
order to brake the vehicle 100. The input rod 205 moves in response
to user input. In self-driving vehicles, the input rod 205 may be
moved with no input from a user (for example, receiving a brake
request from a separate electronic controller). Instead, the input
rod 205 may be moved by a motor, or may not be moved at all. If the
input rod 205 is not moved at all, the electronic controller 115
may receive the brake request from the separate electronic
controller in order to actuate the electromechanical braking
mechanism 110.
The travel sensor 210 detects the movement of the input rod 205.
For example, the travel sensor 210 detects how far the input rod
205 moves from a starting position. The travel sensor 210 is
communicatively coupled to the electronic controller 115 and sends
the distance traveled by the input rod 205 to the electronic
controller 115.
The electronic controller 115 determines control signals for the
permanent magnet synchronous machine 215 (for example, determining
a torque of the permanent magnet synchronous machine 215 based upon
the distance traveled by the input rod 205 received from the travel
sensor 210). The permanent magnet synchronous machine 215 is
configured to move the gear system 220. The gear system 220
converts a torque of the permanent magnet synchronous machine 215
into boost power for the boost element 225. The boost element 225
then applies force based upon the boost power to the master
cylinder 230, where the applied force is converted into hydraulic
pressure to actuate the brakes 120-123.
In a closed loop control system for the electromechanical braking
mechanism 110, the electromechanical braking mechanism 110 may
include sensors that detect a position of a rotor of the permanent
magnet synchronous machine 215 (a rotor position sensor) and a
sensor that detects a current of the permanent magnet synchronous
machine (a motor current sensor). These sensors are used as
feedback mechanisms for the electronic controller 115 as described
below.
In some embodiments, the master cylinder 230 also includes a master
cylinder pressure sensor. The master cylinder pressure sensor
detects a hydraulic pressure in the master cylinder. The master
cylinder pressure sensor may be communicatively coupled to the
electronic controller 115 and may also be configured to send the
hydraulic pressure of the master cylinder 230 to the electronic
controller 115.
The electronic controller 115 is illustrated in FIG. 3 according to
one embodiment. The electronic controller 115 includes an
input-output interface 310, an electronic processor 320 (such as a
programmable electronic microprocessor, microcontroller, and
similar device), and a memory 330 (for example, non-transitory,
machine-readable memory). The electronic processor 320 is
communicatively coupled to the memory 330 and the input-output
interface 310. The electronic processor 320, in coordination with
the memory 330 and the input-output interface 310, is configured to
implement, among other things, the methods described herein.
It is to be understood that the electronic controller 115 may
include a plurality of electrical and electronic components that
provide power, operation control, and protection to the components
and modules within the electronic controller 115 that are not
described herein.
The electronic controller 115 may be implemented in several
independent controllers (for example, programmable electronic
control units) each configured to perform specific functions or
sub-functions. Additionally, the electronic controller 115 may
contain sub-modules that include additional electronic processors,
memory, or application-specific integrated circuits (ASICs) for
handling input/output functions, processing of signals, and
application of the methods listed below. In other embodiments the
electronic controller 115 includes additional, fewer, or different
components.
FIG. 4 illustrates a closed loop control system 400 for the
electromechanical braking mechanism 110. The closed loop control
system 400 is implemented using the electronic controller 115. For
example, a high level closed loop controller 405 may be implemented
as a sub-controller or a microprocessor within the electronic
controller 115 or as a set of software instructions stored in the
memory 330. The high level closed loop controller 405 receives a
signal from the travel sensor 210 indicating how far the input rod
205 has traveled. Based upon the distance traveled, the high level
closed loop controller 405 determines a target motor speed ("Target
Motor Speed") for the permanent magnet synchronous machine 215.
The high level closed loop controller 405 sends the target motor
speed to a closed loop motor speed controller 410. Like the high
level closed loop controller 405, the closed loop motor speed
controller 410 may be implemented as a sub-controller or
microprocessor in the electronic controller 115, or as software
instructions stored in the memory 330. The closed loop motor speed
controller 410 receives the target motor speed and determines,
based upon the target motor speed, a target motor torque.
The closed loop motor speed controller 410 sends the target motor
torque ("Target Motor Torque") to a field-oriented controller 415
(implemented in a similar manner to the high level closed loop
controller 405). The field-oriented controller 415 relies on a
voltage measurement 416 from a power supply, a motor current
measurement 417 from the motor current sensor, and a rotor position
measurement 418 from the rotor position sensor. The field-oriented
controller 415 outputs a duty cycle indicating a target voltage for
each of three phases of the permanent magnet synchronous machine
215 based upon the target motor torque, the voltage measurement
416, the motor current measurement 417, and the rotor position
measurement 418. The duty cycles of each of the three phases
generate a stator voltage space vector, which determines the motor
torque and the rotation of the rotor.
The stator voltage space vector is sent to the permanent magnet
synchronous machine 215, which applies the motor torque to the gear
system 220, which in turn creates an output force and output stroke
420 at the boost element 225. This output force and output stroke
420 is applied to the master cylinder 230, increasing hydraulic
pressure in the master cylinder 230 and applying the hydraulic
pressure to the brakes 120-123 (at block 425).
In some embodiments, the created hydraulic pressure is measured by
a master cylinder pressure sensor as a master cylinder hydraulic
pressure measurement (430), which is then used as feedback by the
high level closed loop controller 405. For example, the high level
closed loop controller 405 may determine an expected hydraulic
pressure based upon the target motor speed. The high level closed
loop controller 405 then compares the received master cylinder
hydraulic pressure measurement 430 to the expected hydraulic
pressure to determine if the components of the electromechanical
braking mechanism 110 are operating correctly.
The closed loop motor speed controller 410 also receives the rotor
position measurement 418. This allows for a more accurate target
motor torque calculation.
The field-oriented controller 415 relies on accurate measurements,
such as the rotor position measurement 418, from the various
sensors it receives signals from in order to apply the correct
amount of braking force received from a brake request (through the
input rod 205 or another brake request). For example, if the motor
current sensor is not working properly or if the rotor position
sensor is not working properly, the field-oriented controller 415
will not be able to provide the correct duty cycles to the
permanent magnet synchronous machine 215. This will cause an
incorrect amount of braking force to be applied to the brakes
120-123.
In order to provide redundancy and a failsafe system in case one or
more sensors fail, an open-loop control system 500 is required.
Such an open-loop control system 500 is illustrated in FIG. 5.
The electronic controller 115 is configured to determine if one or
more sensors (in particular, the motor current sensor and the rotor
position sensor) are not working correctly. For example, the
electronic controller 115 is configured to determine when one or
more sensors are not sending a signal to the electronic controller
115. In another example, the electronic controller 115 may be
receiving feedback from the one or more sensors, but the one or
more sensors are sending data back to the electronic controller 115
that, when compared to an expected value (such as a pressure value
in the master cylinder 230), is determined to be an incorrect
value.
The open-loop control system 500 still utilizes the high level
closed loop controller 405 to determine a target motor speed for
the permanent magnet synchronous machine 215 as described above.
However, because one or more sensors (such as the motor current
sensor or the rotor position sensor) are not working correctly, the
closed loop motor speed controller 410 and the field-oriented
controller 415 may not be able to correctly operate.
In the case that the closed loop motor speed controller 410 and/or
the field-oriented controller 415 are not operating correctly, the
electronic controller 115 determines a target motor speed ("Target
Motor Speed") (using the high level closed loop controller 405) and
determine a target motor speed gradient limitation (block 505).
Because the electronic controller 115 is not receiving feedback
from the motor current sensor or the rotor position sensor, the
electronic controller 115 determines a maximum speed limit and a
maximum amount of allowable change in speed for the permanent
magnet synchronous machine 215. As described below, if the target
motor speed is too high (for example, beyond an operating range of
a stator magnetic field of the permanent magnet synchronous machine
215), the rotor of the permanent magnet synchronous machine 215 may
rotate asynchronously with the stator magnetic field of the
permanent magnet synchronous machine 215, causing incorrect braking
behavior.
In order to operate the permanent magnet synchronous machine 215
when the motor current sensor and/or the rotor position sensor are
not working, the electronic controller 115 generates a control
signal to control the permanent magnet synchronous machine 215 to
create a stator magnetic field. The stator magnetic field is
created with a specified angular velocity (specified by the
electronic controller 115).
The stator magnetic field, when generated by the permanent magnet
synchronous machine 215, causes the rotor of the permanent magnet
synchronous machine 215 to rotate. The stator magnetic field
rotates with the specified angular velocity and the rotor of the
permanent magnet synchronous machine 215 rotates synchronously with
the stator magnetic field. The electronic controller 115, when the
permanent magnet synchronous machine 215 generates the stator
magnetic field, operates the rotor of the permanent magnet
synchronous machine 215 as a stepper motor. For each stepwise
change in a rotating field axis of the stator magnetic field, the
rotor of the permanent magnet synchronous machine 215 changes
position to a position of the rotating field axis.
Due to inertia and friction forces, the rotor of the permanent
magnet synchronous machine 215 may be delayed in following the
position of the rotating field axis. In order to prevent or
minimize this delay, a change rate of the angular velocity of the
stator magnetic field (a frequency of the stator magnetic field)
needs to be limited by target motor speed gradient limitation
505.
The permanent magnet synchronous machine 215 faces a load torque
when applying hydraulic pressure (using the gear system 220 and the
boost element 225) to the master cylinder 230. As the load torque
increases, the rotor of the permanent magnet synchronous machine
215 may begin to lag behind the rotating field axis, following the
rotating field axis at an angle. For example, while the rotor of
the permanent magnet synchronous machine 215 is still rotating
synchronously with the rotating field axis, the position of the
rotor follows the position of the rotating field axis at an angle
(such as 10 degrees behind the position of the rotating field axis)
at the same angular velocity as the stator magnetic field. As long
as an internal torque of the permanent magnet synchronous machine
215 is greater than the load torque, the rotor follows the rotating
field axis synchronously, but at an angle.
In order to ensure that the internal torque of the permanent magnet
synchronous machine 215 is always higher than a load torque (and
therefore to ensure that the rotor of the permanent magnet
synchronous machine 215 is not asynchronous with the rotating field
axis of the stator magnetic field), the frequency of the stator
magnetic field and a stator magnetic flux strength of the stator
magnetic field are selected so that there is enough internal torque
to handle the brake request. The electronic controller 115
therefore determines the frequency of the stator magnetic field and
a stator voltage space vector (at block 510) based upon the
determined stator magnetic flux strength, which is used to operate
the permanent magnet synchronous machine 215, and therefore control
the internal torque of the permanent magnet synchronous machine
215.
Two different design variants allow for the electronic controller
115 to control the internal torque of the permanent magnet
synchronous machine 215. The first design variant allows for the
electronic controller 115 to receive, from a master cylinder
pressure sensor, a hydraulic pressure of the master cylinder 230
(at block 515). The hydraulic pressure is a measure of a pressure
in the master cylinder 230, which indicates how much load the
permanent magnet synchronous machine 215 experiences when applying
pressure (through the gear system 220 and boost element 225) to the
master cylinder 230. Based upon the hydraulic pressure, the
electronic controller 115 determines the frequency of the stator
magnetic field and the stator magnetic flux strength of the stator
magnetic field that is then generated by the permanent magnet
synchronous machine 215.
The stator magnetic flux strength is determined based upon a stator
space vector current, which is in turn based upon a stator voltage
space vector length.
The second design variant includes the electronic controller 115
creating a stator voltage space vector with a fixed length, which
in turn causes the stator magnetic flux strength to be fixed. For
example, the stator voltage space vector length may be fixed so
that the internal torque of the permanent magnet synchronous
machine 215 is always greater than a pressure (load torque) of the
master cylinder 230 would require.
In some embodiments, if the target motor speed gradient limit is
reached, the electronic controller 115 sets a flag (block 520) to
not request more motor speed. For example, once the target motor
speed gradient is determined, the electronic controller 115 may
request an amount of motor speed that is less than the limit (for
example, for a brake request that does not require a large motor
speed). If a new brake request is received by the electronic
controller 115 (for example, the input rod 205 is further depressed
by an operator of the vehicle 100), the electronic controller 115
may then request a faster motor speed. However, if the target motor
speed gradient is reached, the electronic controller 115 sets the
flag at block 520. If a new brake request is received after the
flag is set, the electronic controller 115 will not request a
higher motor speed. A request for a speed higher than the target
motor speed gradient limit may cause the rotor of the permanent
magnet synchronous machine 215 to become asynchronous with the
rotating field axis of the stator magnetic field produced by the
permanent magnet synchronous machine 215.
In some embodiments, the electronic controller 115 determines the
target motor speed gradient limitation based in part upon a power
supply voltage from a power supply motor (at block 525). For
example, if less power is available for the permanent magnet
synchronous machine 215, the target motor speed gradient limitation
may be lower in order to compensate for less power being available
to apply a torque to the permanent magnet synchronous machine
215.
Thus, embodiments described herein generally provide systems and
methods of implementing open loop motor control for an
electromechanical brake when closed loop motor control fails.
Various features, advantages, and embodiments are set forth in the
following claims.
* * * * *